Otilonium is a musculotropic spasmolytic agent belonging to the family of quaternary ammonium derivatives and successfully used in the treatment of patients affected by Irritable bowel syndrome (IBS) due to its specific pharmacokinetic and pharmacodynamic properties. The positive polarity of the head of the Otilonium molecule determines the main pharmacokinetic property of this drug: a minimal systemic absorption and the consequently high safety profile. Studies on animal models revealed a specific Otilonium accumulation in colonic circular muscle at therapeutic µm concentrations, while its plasma levels were 1000 times lower, together with a poor penetration of the drug in the central nervous system. Consistently, after oral administration to healthy volunteers, the Otilonium plasmatic concentration was very low, less than 1% of the drug was eliminated by urine, and 97% was eliminated by feces. Recent clinical studies showed comparable safety and tolerability for Otilonium and placebo. Otilonium was shown to inhibit the main patterns of human sigmoid motility in vitro, including: the tone of smooth muscle cells (SMCs); the rhythmic phasic contractions induced by the interstitial cells of Cajal; and the strong contractions induced by stimulation of enteric motor neurons mainly by blocking the calcium influx through L-type calcium channels on SMCs. Recent in vitro studies using cultured human colonic SMCs to further assess the musculotropic spasmolytic properties of Otilonium confirmed that this drug causes smooth muscle relaxation through the inhibition of voltage-gated calcium channels (L-type > T-type) and the inhibition of muscarinic and tachykinergic effects.